$\begingroup$There is a very good question about indicated air speed vs true air speed on here somewhere that I think will help you a lot. Essentially it matters what you're speed is relative to.$\endgroup$
– Notts90Feb 23 '17 at 8:05

$\begingroup$@mins I think the wind one is the primary.$\endgroup$
– Notts90Feb 23 '17 at 8:06

$\begingroup$Your English is better than some native speakers I know ;)$\endgroup$
– SimonFeb 23 '17 at 8:50

2

$\begingroup$A useful thing to remember is that the aircraft does not know, or care, how fast it is moving over the ground. Imagine you could somehow make the Earth disappear but leaving everything else at it is. The aircraft would still fly perfectly happily.$\endgroup$
– SimonFeb 23 '17 at 9:40

If the UAV velocity is 10 m/s and the stall speed is 10 m/s the plane is at its limit of flying no matter what the wind speed is (neglecting turbulences). The relative speed of the plane and the air is crucial, this speed is mandatory for the physics beyond the lift.

There is simple equation how to calculate sum velocities. Note that they are vectors (speed and direction) not just numbers. $V_{wind}$ can be named as drift velocity.

If the wind direction is opposite to the plane direction its ground speed, at the stall limit, is smaller than the UAV limit. It can be zero (the plane seems stand still) or even negative (plane seems to reverse).

Side notes: $V_{uav}$ is The velocity a pilot cares the most, $V_{ground}$ is the velocity his manager cares. This wind effect is also the reason why flying wit tailwind is preferred by airlines - they spare fuel - and it is also the reason why takeoff and landing is preferred in headwind - you need shorter runway to start/land sucesfully. With tailwind the runway may not be long enough.

$\begingroup$Thanks for your answer . If the plane reduce fuel consuming. (takeoff and landing in headwind) Would please recommend paper or reference for Thrust power of a plane in wind effects?$\endgroup$
– user20115Feb 23 '17 at 15:23